1. Field of the Invention
The present invention relates to a trigger switch used for power tools.
2. Background Art
There are widely used trigger switches mounted on a grip of an power tool or the like and enabling the power tool to be started when a user puts a finger thereon to pull in the same.
As described in JP-A-10-69838, in conventional trigger switches, a contact drive part provided on one end of an operating shaft with a trigger on the other end drives a moving contact to cause the moving contact to come into pressure contact or away from a stationary contact, whereby the circuit is closed and opened.
However, power tools are frequently handled roughly, and an impact force in a bending direction often acts on an operating shaft to cause a danger that the operating shaft is broken at a base end thereof toward a contact drive part. Therefore, with conventional trigger switches, a contact drive part is formed integral with an operating shaft and a trigger is fixed to the an operating shaft afterward in order to ensure a strength for a base end of the operating shaft, on which an external force is liable to be concentrated. Also, the operating shaft is normally biased in a manner to project outward (toward a trigger). Therefore, when a user pulls a trigger with a finger and quickly separates a finger from the trigger from a state, in which the operating shaft is pushed in, the operating shaft is rapidly moved to cause a fear that the trigger is disengaged by an impact at that time, so that it is also necessary to fix the trigger to the operating shaft firmly.
Also, since power tools are frequently used in an environment with much dust, trigger switches are demanded to have a dustproof construction, in which dust does not enter inside. Since an operating shaft comes in and out of a trigger switch, an air having a volume equal to that of the operating shaft, which comes in and out, comes in and out of the trigger switch. Such entrance and exit of an air causes a danger of carrying dust into the switch, it is not preferable to make the operating shaft thick, which degrades the dustproof property of a trigger switch. Also, when an operating shaft is made metallic in order to heighten its strength, design becomes difficult since there is a danger of short-circuiting of an electric circuit inside a trigger switch.
As described above, conventional trigger switches involve a problem that when the dustproof capacity is ensured, an operating shaft is not adequate in strength and in some cases broken by an impact.